Intride-based semiconductor light emitting diode and method of manufacturing the same

ABSTRACT

A nitride-based semiconductor LED includes a substrate; an n-type nitride semiconductor layer formed on the substrate; an active layer and a p-type nitride semiconductor layer that are sequentially formed on a predetermined region of the n-type nitride semiconductor layer; a transparent electrode formed on the p-type nitride semiconductor layer; a p-electrode pad formed on the transparent electrode, the p-electrode pad being spaced from the outer edge line of the p-type nitride semiconductor layer by 50 to 200 μm; and an n-electrode pad formed on the n-type nitride semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.11/543,798, filed Oct. 6, 2006, and claims the benefit of Korean PatentApplication No. 2005-94453 filed with the Korea Industrial PropertyOffice on Oct. 7, 2005, the disclosures of each of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nitride-based semiconductor lightemitting diode (LED). In the nitride-based semiconductor LED, an areaaround a p-electrode pad, in which light is preferentially emitted, isexpanded so as to enhance light extraction efficiency, and local currentcrowding is prevented so as to reduce a driving voltage.

2. Description of the Related Art

Because group III-V nitride semiconductors such as GaN have excellentphysical and chemical properties, they are considered as essentialmaterials of light emitting devices, for example, light emitting diodes(LEDs) or laser diode (LDs). The LEDs or LDs formed of the group III-Vnitride semiconductors are widely used in the light emitting devices forobtaining blue or green light. The light emitting devices are applied tolight sources of various products, such as household appliances,electronic display boards, and lighting devices. Generally, the groupIII-V nitride semiconductors are comprised of gallium nitride (GaN)based materials having an compositional formula ofIn_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, X+Y≦1).

Hereinafter, a conventional nitride-based semiconductor LED will bedescribed in detail with reference to FIGS. 1 and 2.

FIG. 1 is a sectional view illustrating the conventional nitride-basedsemiconductor LED, and FIG. 2 is a plan view illustrating theconventional nitride-based semiconductor LED.

As shown in FIG. 1, the nitride-based semiconductor LED 100 includes asapphire substrate 101 for growing nitride-based semiconductormaterials, an n-type nitride semiconductor layer 102, an active layer103, and a p-type nitride semiconductor layer 104, which aresequentially formed on the sapphire substrate 101. Portions of thep-type nitride semiconductor layer 104 and the active layer 103 areremoved by a mesa etching process, so that the n-type nitridesemiconductor layer 102 is partially exposed.

On the p-type nitride semiconductor layer 104 which has not been etchedby the mesa etching process, a p-electrode pad 106 is formed. On then-type nitride semiconductor layer 102, an n-electrode pad 107 isformed.

Since the p-type nitride semiconductor layer 104 has larger specificresistance than the n-type nitride semiconductor layer 102, a differencein resistance between the p-type nitride semiconductor layer 104 and then-type nitride semiconductor layer 102 causes a current spreading effectto be reduced. As such, when a current spreading effect decreases, lightextraction efficiency also decreases so that the brightness of thenitride semiconductor LED 100 is reduced. Accordingly, in order toenhance a current spreading effect in the related art, a transparentelectrode 105 is formed on the p-type nitride semiconductor layer 104 soas to increase an injection area of current which is injected throughthe p-electrode pad 106.

In the above-described nitride-based semiconductor LED 100, thetransparent electrode 105 is further provided on the p-type nitridesemiconductor 104 so as to obtain an enhanced current spreading effect.However, when a difference in surface resistance between the transparentelectrode 105 and the n-type nitride semiconductor layer 102 is large, acurrent spreading effect is still small. For example, when acommonly-used ITO (indium tin oxide) is used as the transparentelectrode 105, local current crowding occurs in the vicinity (refer toreference numeral ‘A₁’) of the p-electrode pad because of high surfaceresistance of the ITO.

In the nitride-based semiconductor LED 100, the p-electrode pad 106 isformed as close to the outer edge line of the p-type nitridesemiconductor layer 104 as possible, the outer edge line being a mesaline. Further, the p-electrode pad 106 and the n-electrode 107 is spacedat the maximum distance from each other so as to secure the maximumlight emitting area therebetween. Then, an optical output is expected tobe enhanced. In this case, however, local current crowding increases inthe vicinity (A₁) of the p-electrode pad 106, thereby degrading thereliability of the diode.

The vicinity (A₁) of the p-electrode pad 106 is a region (hereinafter,referred to as ‘preferential light emission region’) in which light ispreferentially emitted. When the p-electrode pad 106 is formed close tothe mesa line, there is a limit in securing an area in the vicinity (A₁)of the p-electrode pad 106 which is a preferential light-emission regionof which the luminous density is high. Such a limit makes it difficultto enhance the light extraction efficiency of the entire chip. In themeantime, a dotted line of FIG. 1 represents a current path.

SUMMARY OF THE INVENTION

An advantage of the present invention is that it provides anitride-based semiconductor light emitting diode (LED) in which an areaaround a p-electrode pad is expanded so as to enhance light extractionefficiency, and local current crowding is prevented so as to reduce adriving voltage, in order to enhance the reliability of the diode.

Additional aspect and advantages of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the general inventive concept.

According to an aspect of the invention, a nitride-based semiconductorLED comprises a substrate that is formed in a rectangle shape and ofwhich a ratio of the width and the length is equal to or more than 1.5;an n-type nitride semiconductor layer that is formed on the substrateand is composed of an n-type semiconductor material having acompositional formula of In_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, and X+Y≦1);an active layer and a p-type nitride semiconductor layer that aresequentially formed on a predetermined region of the n-type nitridesemiconductor layer, the active layer being composed of a semiconductormaterial having a compositional formula of In_(X)Al_(Y)Ga_(1-X-Y)N (0≦X,0≦Y, and X+Y≦1) and the p-type nitride semiconductor layer beingcomposed of a p-type semiconductor material having a compositionalformula of In_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, and X+Y≦1); a transparentelectrode that is formed on the p-type nitride semiconductor layer so asto be spaced at a predetermined distance from the outer edge line of thep-type nitride semiconductor layer; a p-electrode pad that is formed onthe transparent electrode so as to be spaced at a distance of 50 to 200μm from the outer edge line of the p-type nitride semiconductor layercomposed of a p-type semiconductor material having a compositionalformula of In_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, and X+Y≦1); and ann-electrode pad that is formed on the n-type nitride semiconductorlayer.

The nitride-based semiconductor LED further comprises a buffer layerthat is formed between the substrate and the n-type nitridesemiconductor layer and is composed of AlN/GaN. The substrate is asapphire substrate.

Preferably, the n-type nitride semiconductor layer is a GaN layer orGaN/AlGaN layer doped with any one n-type conductive impurity selectedfrom the group consisting of Si, Ge, and Sn, the p-type nitridesemiconductor layer is a GaN layer or GaN/AlGaN layer doped with any onep-type conductive impurity selected from the group consisting of Mg, Zn,and Be, and the active layer is composed of an InGaN/GaN layer with amulti-quantum well structure.

Preferably, the transparent electrode is an ITO (Indium Tin Oxide)material.

Preferably, the p-electrode pad and the n-electrode pad are formed of Auor Au/Cr.

When the p-electrode pad is spaced at a distance of 50 to 200 μm fromthe outer edge line of the p-type nitride semiconductor layer, opticalpower may increase.

When the p-electrode pad is spaced at a distance of more than 200 μmfrom the outer edge line of the p-type nitride semiconductor layer,optical power may decrease.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawings will be provided by the Office upon request and paymentof the necessary fee.

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1 is a sectional view illustrating a conventional nitride-basedsemiconductor LED;

FIG. 2 is a plan view illustrating the conventional nitride-basedsemiconductor LED;

FIG. 3 is a sectional view illustrating a nitride-based semiconductorLED according to an embodiment of the present invention;

FIG. 4 is a plan view illustrating the nitride-based semiconductor LEDaccording to the embodiment of the invention;

FIGS. 5A to 5D are sectional views for explaining a method ofmanufacturing the nitride-based semiconductor LED according to anembodiment of the invention;

FIG. 6 is a graph illustrating a change in Po (optical power) inaccordance with a separation distance of a p-electrode pad;

FIG. 7 is a graph illustrating a change in a driving voltage inaccordance with a separation distance of the p-electrode pad; and

FIG. 8 is a color photograph showing a state where the p-electrode padis spaced from a mesa-line by 55 μm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to likeelements throughout. The embodiments are described below in order toexplain the present general inventive concept by referring to thefigures.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

Structure of Nitride-Based Semiconductor LED

Referring to FIGS. 3 and 4, a nitride-based semiconductor LED accordingto an embodiment of the invention will be described in detail.

FIG. 3 is a sectional view illustrating the nitride-based semiconductorLED, and FIG. 4 is a plan view illustrating the nitride-basedsemiconductor LED.

As shown in FIG. 3, the nitride-based semiconductor LED 200 according tothe embodiment of the invention includes a sapphire substrate 201 forgrowing nitride-based semiconductor materials, a buffer layer (notshown), an n-type nitride semiconductor layer 202, an active layer 203,and a p-type nitride semiconductor layer 204, which are sequentiallyformed on the sapphire substrate 201. Portions of the p-type nitridesemiconductor layer 204 and the active layer 203 are removed by a mesaetching process, so that the upper surface of the n-type nitridesemiconductor layer 202 is partially exposed.

The buffer layer is grown on the sapphire substrate 201 so as to enhancethe lattice matching between the sapphire substrate 210 and the n-typenitride semiconductor layer 202. The buffer layer may be formed ofAlN/GaN or the like.

The n-type and p-type nitride semiconductor layers 202 and 204 and theactive layer 203 can be formed of a semiconductor material having acompositional formula of In_(X)Al_(Y)Ga_(1-X-Y)N (here, 0≦X, 0≦Y, andX+Y≦1). More specifically, the n-type nitride semiconductor layer 202can be formed of a GaN or GaN/AlGaN layer doped with n-type conductiveimpurities. For example, the n-type conductive impurity may be Si, Ge,Sn and the like, among which Si is preferably used. Further, the p-typenitride semiconductor layer 204 can be formed of a GaN or GaN/AlGaNlayer doped with p-type conductive impurities. For example, the p-typeconductive impurity may be Mg, Zn, Be and the like, among which Mg ispreferably used. The active layer 203 can be formed of an InGaN/GaNlayer with a multi-quantum well structure.

On the p-type nitride semiconductor layer 204 which has not been removedby the mesa-etching process, a transparent electrode 205 is formed of anITO material. As shown in FIG. 3, the transparent electrode 205 isspaced at a predetermined distance from the outer edge line of thep-type nitride semiconductor layer 204. On the transparent electrode205, a p-type electrode pad 206 is formed so as to be spaced at apredetermined distance from the outer edge line of the p-type nitridesemiconductor layer 204 which is a mesa line. On the n-type nitridesemiconductor layer 202 exposed by the mesa etching process, an n-typeelectrode pad 207 is formed. At this time, it is preferable that thep-type electrode pad 206 is formed so as to be spaced from the outeredge line of the p-type nitride semiconductor layer 204 by 50 to 200 μm,in consideration of the size of a general nitride-based semiconductorLED chip.

As shown in FIG. 4, the plan shape of the substrate 201 is formed in arectangle shape. In this case, it is preferable that a ratio of thewidth to the length of the rectangle is 1:1.5.

In the meantime, when a commonly-used ITO is used as the transparentelectrode 205 as described above, local current crowding can occur inthe vicinities of the p-type electrode pad 206 because of high surfaceresistance of the ITO. In this embodiment, however, the p-type electrodepad 206 is spaced at a predetermined distance from the mesa line, whichmakes it possible to reduce local current crowding. Accordingly, it ispossible to enhance the reliability of the diode (for example, a drivingvoltage can be reduced) and to expand an area around the p-electrode pad206 which is a preferential light emitting region (refer to referencenumeral ‘A₂’ of FIG. 3). Therefore, it is possible to enhance theoverall light emission efficiency of the chip. Meanwhile, a dotted lineof FIG. 3 shows a current path.

Method of Manufacturing Nitride-Based Semiconductor LED

Hereinafter, a method of manufacturing a nitride-based semiconductor LEDaccording to an embodiment of the invention will be described.

FIGS. 5A to 5D are sectional views illustrating the method ofmanufacturing a nitride-based semiconductor LED.

First, as shown in FIG. 5A, a buffer layer (not shown), an n-typenitride semiconductor layer 202, an active layer 203, and a p-typenitride semiconductor layer 204 are sequentially formed on a sapphiresubstrate 201 for growing nitride-based semiconductor materials. Thebuffer layer may be omitted, and the n-type nitride semiconductor layer202, the active layer 203, and the p-type nitride semiconductor layer203 can be formed of a semiconductor material having a compositionalformula of In_(X)Al_(Y)Ga_(1-X-Y)N (here, 0≦X, 0≦Y, and X+Y≦1). Ingeneral, they may be formed through such a process as a metal organicchemical vapor deposition (MOCVD) method.

Next, as shown in FIG. 5B, portions of the p-type nitride semiconductorlayer 204, the active layer 203, and the n-type nitride semiconductorlayer 202 are mesa-etched so as to partially expose the n-type nitridesemiconductor layer 202.

As shown in FIG. 5C, a transparent electrode 205 is formed on the p-typenitride semiconductor layer 204. In general, the transparent electrode205 is formed of an ITO.

As shown in FIG. 5D, a p-electrode pad 206 is formed on the transparentelectrode 205 spaced at a predetermined distance from the outer edgeline of the p-type nitride semiconductor layer 204, and an n-electrodepad 207 is formed on the n-type nitride semiconductor layer 202. Thep-electrode pad 206 and the n-electrode pad 207 may be formed of metalsuch as Au or Au/Cr.

As described above, current crowding can occur in the vicinities of thep-electrode pad 206 because of high surface resistance of an ITO used asthe transparent electrode 205. In this embodiment, however, thep-electrode pad 206 is spaced at a predetermined distance from the mesaline, which makes it possible to reduce local current crowding.Therefore, a driving voltage can be reduced, and an area around thep-electrode pad 206 which is a preferential light emitting region can beexpanded (refer to reference numeral ‘A₂’ of FIG. 5D), which makes itpossible to enhance the overall light emission efficiency of the chip.

FIG. 6 is a graph illustrating a change in Po (optical power) inaccordance with a separation distance of the p-electrode pad, and FIG. 7is a graph illustrating a change in a driving voltage in accordance witha separation distance of the p-electrode pad.

Referring to FIG. 6, while the p-electrode pad 206 is spaced from themesa line by 50 to 200 μm, Po tends to increase. As the p-electrode pad206 is spaced from the mesa line by more than 200 μm, Po decreases.Therefore, it is most preferable that the p-electrode pad 206 is spacedfrom the outer edge line of the p-type nitride semiconductor layer 204as the mesa line by 50 to 200 μm. Further, referring to FIG. 7, as thep-electrode pad 206 is spaced at a predetermined distance from the mesaline, that is, as the distance between the p-electrode pad 206 and then-electrode pad 207 is reduced, a driving voltage is reduced.

FIG. 8 is a color photograph showing a luminous state when thep-electrode pad is spaced from the mesa line by 55 μm.

When the p-electrode pad 206 is spaced from the mesa line by 55 μm, auniform luminous effect can be obtained in the entire chip, as shown inFIG. 8. Further, an area around the p-electrode pad 206, which is apreferential light emitting region, can be expanded, so that the overallluminous efficiency of the chip can be further enhanced.

Preferably, the plan shape of the sapphire substrate 201 is formed in arectangle shape. This is because, when the sapphire substrate 201 isrectangular, it is advantageous to secure a margin of distance where thep-electrode pad 206 can be spaced from the mesa line, compare with whenthe sapphire substrate 201 is formed in a square shape. In this case, itis preferable that a ratio of the width to the length of the rectangleis 1:1.5. This is because, when a ratio of the width to the length ofthe rectangle is less than 1.5, the p-electrode pad 206 spaced from themesa line becomes so close to the n-electrode pad 207 that a currentspreading effect can be reduced.

According to the nitride-based semiconductor LED and the method ofmanufacturing the same of the present invention, the p-electrode pad isspaced at a predetermined distance from the mesa line, and an areaaround the p-electrode pad, in which light is preferentially emitted, isexpanded so as to enhance light extraction efficiency of a chip.Further, local current crowding is reduced so as to reduce a drivingvoltage, thereby enhancing the reliability of the diode.

Although a few embodiments of the present general inventive concept havebeen shown and described, it will be appreciated by those skilled in theart that changes may be made in these embodiments without departing fromthe principles and spirit of the general inventive concept, the scope ofwhich is defined in the appended claims and their equivalents.

1-6. (canceled)
 7. A nitride-based semiconductor LED comprising: asubstrate that is formed in a rectangle shape and of which a ratio ofthe width and the length is equal to or more than 1.5; an n-type nitridesemiconductor layer that is formed on the substrate and is composed ofan n-type semiconductor material having a compositional formula ofIn_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, and X+Y≦1); an active layer and ap-type nitride semiconductor layer that are sequentially formed on apredetermined region of the n-type nitride semiconductor layer, theactive layer being composed of a semiconductor material having acompositional formula of In_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, and X+Y≦1)and the p-type nitride semiconductor layer being composed of a p-typesemiconductor material having a compositional formula ofIn_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, and X+Y≦1); a transparent electrodethat is formed on the p-type nitride semiconductor layer so as to bespaced at a predetermined distance from the outer edge line of thep-type nitride semiconductor layer; a p-electrode pad that is formed onthe transparent electrode so as to be spaced at a distance of 50 to 200μm from the outer edge line of the p-type nitride semiconductor layercomposed of a p-type semiconductor material having a compositionalformula of In_(X)Al_(Y)Ga_(1-X-Y)N (0≦X, 0≦Y, and X+Y≦1); and ann-electrode pad that is formed on the n-type nitride semiconductorlayer.
 8. The nitride-based semiconductor LED according to claim 7further comprising: a buffer layer that is formed between the substrateand the n-type nitride semiconductor layer and is composed of AlN/GaN,wherein the substrate is a sapphire substrate.
 9. The nitride-basedsemiconductor LED according to claim 7, wherein the n-type nitridesemiconductor layer is a GaN layer or GaN/AlGaN layer doped with any onen-type conductive impurity selected from the group consisting of Si, Ge,and Sn, the p-type nitride semiconductor layer is a GaN layer orGaN/AlGaN layer doped with any one p-type conductive impurity selectedfrom the group consisting of Mg, Zn, and Be, and the active layer iscomposed of an InGaN/GaN layer with a multi-quantum well structure. 10.The nitride-based semiconductor LED according to claim 7, wherein thetransparent electrode is an ITO (Indium Tin Oxide) material.
 11. Thenitride-based semiconductor LED according to claim 7, wherein thep-electrode pad and the n-electrode pad are formed of Au or Au/Cr. 12.The nitride-based semiconductor LED according to claim 7, wherein whenthe p-electrode pad is spaced at a distance of 50 to 200 μm from theouter edge line of the p-type nitride semiconductor layer, optical powerincreases.
 13. The nitride-based semiconductor layer according to claim7, wherein when the p-electrode pad is spaced at a distance of more than200 μm from the outer edge line of the p-type nitride semiconductorlayer, optical power decreases.